Fan coral is a type of coral which develops a highly branched flexible skeleton which often comes to closely resemble a fan, albeit a rather inefficient one. These corals belong to the order Gorgonacea, named for the mythical Gorgon, a figure in Greek mythology closely associated with snakes. Fan corals can resemble tangled clusters of snakes in some cases, which explains the scientific name.
You may hear fan coral referred to as a sea fan or a gorgonian, in a reference to its biological order. As is the case with other corals, a sea fan isn’t a single organism. It is, in fact, a colony of organisms known as polyps which band together and develop a supportive skeleton. In the case of sea fans, the polyps use bromine, iodine, and tyrosine to create a flexible substance known as gorgonin. The surface of the coral tends to be rough and slightly horny, and it is resilient in addition to flexible, ensuring that sea fans can withstand heavy currents.
The color of this coral varies, depending on the species and whether or not symbiotic algae are living inside the sea fan. Colors typically range from yellow to red, with the polyps located along the branching arms of the fan. The polyps have eight tentacles which they use to filter free-floating organisms from the water to eat. They may also feed on the symbiotic algae, if it is present. Because fan coral cannot actively hunt its prey, it requires strong currents to provide enough nutrition.
Fan coral is primarily nocturnal, with the polyps pulling their tentacles in during the day to protect themselves from predators and the potential for sun burn. These corals reproduce by mass-spawning eggs and sperm, which fuse in the water to become gametes. The gametes free-float until they find an area of sand or mud to settle in.
There are over 500 species of fan coral, most of which are found in the Atlantic. These corals can live to be hundreds of years old, and they are very slow growing. This type of coral is also extremely vulnerable to human interference, as careless divers can break off arms, destroying decades of growth, and trawlers routinely rip out the coral as they dredge the bottom of the ocean for fish. Fan corals are also vulnerable to deliberate harvest for commercial profit, and to nutrient runoff, which can trigger algae blooms which cloud the water, making it difficult for fan coral to live.